Surface waters throughout the world are contaminated with nutrients that come from a range of non-point sources (e.g., agricultural and storm water run-off, high-density animal operations, and atmospheric deposition), and inadequately treated wastewaters. Chief among the contaminants is nitrogen, which is present as nitrate (NO3−), nitrite (NO2−), and ammonium (NH4+). Excess concentrations of these nutrients cause eutrophication of natural water bodies, particularly the ocean, estuaries, lakes, and reservoirs. Up to the present time, no reliable means is available to remove these nitrogen-containing compounds from surface water once the water is contaminated from one or more of the sources. Limited removal is possible when the water passes through natural or engineered wetlands, but normally these systems are able to remove only a modest fraction of the total nitrogen load in the surface water.